1.Field of the Invention:
This invention relates to control valve devices in general, and more particularly to a control valve device which controls fluid communication in a fluid passage in response to both an input current signal from a switch device and in response to a signal indicating a change in engine ambient temperature.
2.Discussion of the Background:
Valve devices of the type to which the present invention is directed are particularly well adapted for use in a carburetor outer vent control system of an automotive internal combustion engine and which prevents fuel evaporative gas produced in a carburetor float chamber from being discharged into the atmosphere.
FIG. 2 shows a conventional example of the above-noted carburetor outer vent control system wherein when an engine ignition switch 51 is actuated to start the engine, an electric current is applied to a solenoid coil 53 from a battery 52 as an electric source. As a result, an electromagnetic valve 54 is maintained in a closed position thereby blocking a fuel evaporative gas passage 55. This electromagnetic valve 54 is a normally open type valve which is maintained in an opened state when the switch 51 is in an OFF position. Therefore, the fuel evaporative gases produced in a carburetor float chamber 56 cannot be absorbed on a canister 57 during the engine operation. In this case, the fuel evaporative gases are supplied to the engine through an inner vent tube 58 and an air-fuel induction passage 59 of a carburetor 62, and then are burned.
Next, when the engine is stopped, no electric current is applied to the solenoid coil 53 to thereby maintain the electromagnetic valve in an open position. At this time, the ambient engine temperature still being high, fuel in the float chamber 56 is evaporated. The evaporated fuel gas, namely the fuel evaporative gases, are absorbed in the canister 57 by means of the electromagnetic valve 54 positioned in the fuel evaporative gases passage 55 and by means of the thermal responsive control valve 60, thereby preventing the fuel evaporative gases from being discharged into the atmosphere. The control valve 60 is maintained opened at a high temperature (over approximately 50.degree. C.), and closed at a low temperature, respectively.
As time proceeds after the engine is stopped, the engine temperature falls. When the temperature falls below a predetermined value, the control valve 60 is maintained closed, thereby preventing the fuel evaporative gases from being absorbed in the canister 57. However, since the fuel is only slightly evaporated due to the drop in the fuel temperature within the float chamber 56, such is not a serious problem even if the absorption of the canister is interrupted.
As shown in FIG. 2, the carburetor 62 is, of the downdraft type, having the air-fuel induction passage 59 at one end thereof and connected to an engine intake manifold 63 at the opposite end thereof. The induction passage 59 includes a throttle valve 61 which is rotatably maintained on a part of the carburetor body across the passage 59 in a manner so as to control the flow of the air-fuel mixture into the intake manifold 63.
In the conventional carburetor outer vent control system shown in FIG. 2, however, both the electromagnetic valve 54 operable in response to the ignition switch 51 and the thermal responsive control valve 60 operable in response to changes in the engine temperature are separately constructed. Therefore, the number of parts constituting the control system 50 will increase and the control system 50 thus becomes larger in size, whereby it may be difficult to install the control system 50 on the internal combustion engine. Furthermore, the thermal responsive control valve 60 operates in response to an ambient temperature in the vicinity of the carburetor 62. Since this ambient temperature is not exactly the same as the temperature in the carburetor float chamber 56, with the result that a certain difference in temperature may be observed, the outer vent control system 50 cannot operate with high accuracy in response to changes in temperature of the float chamber 56.